Flexible supercapacitors (FSCs) are limited in flexible electronics applications due to their low energy density. Therefore, developing electrode materials with high energy density, high electrochemical activity, and remarkable flexibility is challenging. Herein, we designed nitrogen-doped porous MXene (N-MXene), using melamine-formaldehyde (MF) microspheres as a template and nitrogen source. We combined it with an electrospinning process to produce a highly flexible nitrogen-doped porous MXene nanofiber (N-MXene-F) as a self-supporting electrode material and assembled it into a symmetrical supercapacitor (SSC). On the one hand, the interconnected mesh structure allows the electrolyte to penetrate the porous network to fully infiltrate the material surface, shortening the ion transport channels; on the other hand, the uniform nitrogen doping enhances the pseudocapacitive performance. As a result, the as-assembled SSC exhibited excellent electrochemical performance and excellent long-term durability, achieving an energy density of 12.78 Wh kg⁻¹ at a power density of 1080 W kg⁻¹, with long-term cycling stability up to 5000 cycles. This work demonstrates the impact of structural design and atomic doping on the electrochemical performance of MXene and opens up an exciting possibility for the fabrication of highly FSCs.